Raster input scanning devices of the type contemplated generally include an array of photoelectric sensors or detectors or photosites arranged across an image scanning field for detecting light from an image; a data transmission and processing system for taking the image data derived from the photoelectric detectors and passing the image information to a data processing system, such as a microprocessor; and a transport for relative movement of the image to be scanned across the scanning field so that photoelectric sensors extending transversely across the image field direction of motion are able to detect on a scan line-by-scan line basis the images on the scanned surface. Of particular interest is the processing of color images. In color image scanning, the scanned image must be broken into component colors, each of which is processed separately for later inclusion with the assimilation of the entire image at a later time. This may be done in a variety of ways. In the past, the entire image was scanned, for example three times, each time with a different color filter superimposed over the scanned image. Thus, each scanning operation produced selected color information based on the filter over the image. In such a system, the detectors are able to detect only the difference between a light and dark image, and may use detectors similar to those detecting only black and white information.
With the development of color filter sensors, which provide photosites with color filters, and the ability to make longer arrays of photosites, it has become possible to provide scanning systems requiring only a single pass of the image. In these systems, a large amount of data is created by the photosites requiring fast handling of the data by image processing systems, and, particularly, within the array itself. Speed in which the document can be read is dependent on the time in which data derived by the photosites can be transmitted to the processing system. For example, if it is desired to move the image surface in a Y-direction at a speed of 1 inch/sec (approximately 2.54 cm/sec), and a resolution of 300 scan lines/inch (approximately 118 scan lines/cm) is desired, it becomes necessary to move data from 300 scan lines of data per second from the photosites to the processor. Since the arrays may range along the X-direction in length from 3500 to in excess of 5100 photosites, it will be appreciated that a large amount of information must be handled to achieve the required processing speed.
A commercial product by Toshiba Corporation, Model No. TCD 112, provides a sensor arrangement having an arrangement including a plurality of arrays in offset and overlapping relationship to cover the X-direction of an image field. This product splits each individual photosite into three sites each with a color filter. Color image information may be derived from the sensors, and is passed in sequential fashion to a data processor. It would be preferable, however, to provide an array with larger photosites since a larger photosite is more sensitive to the light focused thereon and allows the documents to be scanned at a higher rate of speed. Additionally, the overlapping and offset arrangement of the TCD 112 makes it difficult to align the segments. Thus, extensive processing of the signal is required to compensate for the offset alignment of the arrays.